Design and evaluation of biorefinery concepts: Dissertation

When new biorefinery processes are developed, certain challenges are encountered during the research and development stage. There are multiple possible production routes to select from but due to limited information available at this stage it is difficult to assess the reasoning of the selected route especially when it concerns environmental and economic issues. In this thesis, a new modelling approach for this problem was developed. This new method can be used to design, evaluate and select process alternatives in research and process development, thus enhancing process development by enabling making more informed decisions earlier. Firstly, multiple lignocellulosic raw materials, for example those based on wood biomass or straw, and processes were evaluated based on the maximum product yield of the main product for each raw material. Secondly, the best processes were selected for analysis of main and side product energy yields, greenhouse gas (GHG) emission reductions and net present values (NPV), using simplified flowsheet models based on maximum heat recovery. Thirdly, the previous calculations were repeated for the selected processes employing rigorous flowsheet models. At the first modelling level, calculated energy yield of main product was employed as the preliminary indicator, and showed satisfactory accuracy. At the second and third modelling levels the differences of the indicators in main and side product energy yields, differences in GHG emission reductions and NPV are relatively small. The indicators based on second level models can in most cases be used in the early phase of process development. New process concepts that utilise separate lignin and carbohydrate fraction processing, including enhanced methanol and synthetic natural gas and hydrocarbon production, were developed by employing the modelling approach described. They were compared with conventional processes, such as methanol and synthetic natural gas (SNG) production, including combined biochemical ethanol and methanol production via lignin residue. Among the novel processes, hydrocarbon production utilising external low-temperature heat gave the highest product yield, 72.5 %, the highest GHG reduction per year and the lowest costs of GHG reduction when the produced biofuel substitutes fossil fuel. Integration to pulp and paper plants or stand-alone pulp mills was found advantageous since the processes could utilise unused heat, unused bark and the separated lignin from chemical recovery from the pulp mill. The novel processes could be run in two modes: either using external heat and power available in summer from solar economy sources, or self-sufficiently in winter. The processes studied are at an early development stage. Therefore, the performance of the novel processes should be verified with a larger scale experimental study.